Dash lights suddenly not working at night

Usually when that happens to me, I have knocked the dash dimmer wheel a tiny bit with some parcel I was swinging in or out of the car, and turning the dimmer knob back up until the nighttime illumination reappears is how I resolve it.

The only role the light sensor plays is that it keeps the illumination at day level when it's light out (even with the headlights on), but switches to night level (set by the dimmer knob) when it's dark out.

 

Yes, it's strange that the dimmer switch will actually allow you to totally turn-off the dash lamps at night. I had to pull over once and use my cell phone lamp to find the switch to crank it back up. It's not something you develop muscle memory, since it's one of those set it and forget it functions.

 

I think the illumination of the dash comes from sources of different kinds ... probably no incandescent light bulbs anymore in Prius v (though gen 2 had some), but some LEDs, and a vacuum-fluorescent meter display. Those kinds of sources don't all have a steady dimming curve down to zero, and things like temperature probably affect them too. Chances are it'd be hard to build a dimmer control reliably able to take them right down to minimum brightness but without any of them going out. If it worked in summer it might not in winter, or vice versa.

I just replaced a dimmer in my dining room because the old one wasn't designed for LED light bulbs. The new one has a hidden little dial where you can adjust what its minimum output is, to keep it above where the LEDs just go out. Took me a few tries.

 

Once you get below 2 bars on my gen4, there's not illumination. Mine is usually set for 3 bars, so if it gets bumped by my knee - it's out.